Multi-layer polyolefin film containing recycle polymer from cross-linked films

ABSTRACT

A process for the manufacture of a multilayer cross-linked, heat-shrinkable, polyolefin film, said film having at least one inner layer comprising thermo-plastic polymer sandwiched between two outer layers comprised of thermoplastic polymer different from the thermoplastic polymer of said inner layer, comprising the steps of a) coextruding the materials into a tape; b) cross-linking it; c) converting said cross-linked tape into a heat-shrinkable film by orientation; characterized in that scrap material produced in the manufacture or in the further processing to finished articles of cross-linked films of this same structure is incorporated by recycling it into said step a) in an amount up to 50% by weight of the total film weight.

This application is a divisional of Ser. No. 08/427,549 filed Apr. 20,1995 U.S. Pat. No. 5,605,660.

FIELD OF THE INVENTION

The present invention relates to a process of manufacturing heatshrinkable films particularly to the recycling of film scraps in themanufacture of said films.

BACKGROUND OF THE INVENTION

The manufacture of heat-shrinkable films is well known in the art.

As heat-shrinkable film, the expert in the field means a polymeric filmwhich has the ability to shrink or, if restrained from shrinking, togenerate shrink tension within the film.

Heat-shrinkable films are well known in the art and their main field ofapplication is package of food and non-food goods.

The term "film" identifies a flexible thermoplastic sheet with a typicalthickness of from about 10 microns to about 150 microns and preferablyof from about 12 to about 100 microns. When a packaging film to be usedas such in a packaging machine is meant, it will typically have athickness of from about 10 to about 50 microns and preferably of fromabout 12 to about 35 microns, while when the film has first to beheat-sealed to itself, converted into a flexible thermoplastic containerand then used in a packaging machine in the form of a bag or a pouchwhere the good to be packaged is introduced, it will have typically athickness of from about 50 to about 150 microns preferably of from about50 to about 100 microns.

Heat-shrinkable films typically have a multi-layered structurecomprising olefinic polymers and/or copolymers of various kind, and theterms "polymer" or "polymeric resin", as herein used, generally includehomopolymers, copolymers, terpolymers, block polymers, graft polymer,random polymers and alternate polymers.

The manufacture of the above films may generally be accomplished byextrusion (for single layer films) or coextrusion (for multi-layerfilms) of thermoplastic resinous materials which have been heated totheir flow or melting point from one extrusion or coextrusion die in,for example, either tubular or planar (sheet) form. After apost-extrusion quenching to cool by well known systems the relativelythick extrudate is then reheated to a temperature within its orientationtemperature range, generally below the crystalline melting point butabove the second order transition temperature (glass transition point).

The terms "orientation" or "oriented" are used herein to generallydescribe the process step and resultant product characteristics obtainedby stretching and immediately cooling a resinous thermoplastic polymericmaterial, which has been heated to an orientation temperature range soas to revise the molecular configuration of the material by physicalalignment of the crystallites and/or molecules of the material in orderto modify certain mechanical properties to the desired properties, forexample shrink tension and orientation release stress.

The term "oriented" is also used herein interchangeably with the term"heat-shrinkable". An oriented (i.e. heat-shrinkable) material will tendto return to its unstretched (unextended) dimension when heated to anappropriate elevated temperature.

In the basic process for manufacturing the film as above, the film, onceextruded (or coextruded, whenever the case) and initially cooled by, forexample, cascade water or chill roll quenching, is then reheated towithin its orientation temperature range and oriented by stretching.When the stretching force is applied in one direction, uniaxialorientation results. When the stretching force is applied in twodirections, biaxial orientation results. The stretching to orient may beaccomplished in many ways such as for example by "blown bubble"techniques or "tenter framing". These processes are well-known to thoseskilled in the art and refer to orientation procedures whereby thematerial is stretched in the cross or transverse direction (TD) and/orin the longitudinal or machine direction (MD). After being stretched,the film is rapidly cooled while substantially retaining its stretcheddimension and thus set or lock-in the oriented (aligned) molecularconfiguration.

After setting the stretch-oriented molecular configuration, the film maythen be stored in rolls and utilized to tightly package a wide varietyof items.

The above general outline of manufacturing of films is not meant to beall inclusive, since such processes are well-known to the expert in theart. Examples of these processes are disclosed in Italian patent n.1163118 and U.S. Pat. No. 4551380, both in the name of the applicant;said patents also refers to a number of documents relating to the priorart, for example U.S. Pat. Nos. 4,274,900; 4,229,241; 4,194,039;4,188,443; 4,048,428; 3,821,182; 3,022,543.

Furthermore, when certain characteristics of the film are to beimproved, the polymeric structure may be modified in a well-known way.In particular cases, cross-linking of the polymeric structure can beperformed, for example by irradiation or chemically. A generaldisclosure of cross-linking can be found, among others, in U.S. Pat. No.4,551,380, assigned to the applicant, issued Nov. 5, 1985.

Cross-linked multi-layered heat shrinkable films are there disclosed andclaimed.

Generally, a considerable amount of scrap is generated in the course ofthe manufacture of heat-shrinkable films, such scraps coming fromtrimming from roll ends, film breakages, filling custom ordersrequesting special width, or rolls out of specification. In the tenterframe biaxial orientation step, considerable scraps come also fromtrimming the film edges in the transversal direction.

Such amount of scraps represents an economical burden and a heavyenvironmental problem due to the waste of plastic material.

A method of recycling coextruded scraps is disclosed in U.S. Pat. No.4,877,682, assigned to Amoco Corporation, issued October 31, 1989. Thispatent discloses laminates containing scraps and further disclosesarticles of manufacture, particularly cookware. The patent relates tothermoplastic materials, which must have particular characteristics asto stiffness and heat-resistance. Among the many exemplary layermaterials, polyolefins are cited, particularly crystallinepolypropylene, crystalline polyethylene of low, medium, preferably highdensity. Crystalline polypropylene is said to be particularly preferredbecause of its high use temperature. The laminates herein disclosed mustbe capable of resisting deformation or deflection at cookingtemperature. Therefore the background of this patent is distant from theone of the present invention which relates to heat-shrinkable films forpackaging use.

The International Application WO 91/17886, in the name of E. I. DupontDe Nemours, published Nov. 28, 1991, discloses a multi-layerheat-shrinkable polymeric film containing recycle polymer.

This document claims a process of coextruding a multi-layerheat-shrinkable film having at least a core layer of thermoplasticpolymer sandwiched between two outer layers and coextruding recycle ofsaid film into said core along with said thermoplastic polymer of saidcore. On p. 2, 1. 30, of WO 91/17886iit is clearly stated that radiationinvolved in making particular heat-shrinkable films prevents scrap fromthe film from being recycled by melt processing, e.g. extrusion. Thisteaching is repeated on p. 8, 1. 22, as the scrap must be meltprocessable, hence the original heat shrinkable film from which thescrap was obtained must be free of crosslinking, such as from radiation,which would prevent melt processing.

Definitions

In the present description, unless specifically set forth and defined orotherwise limited, the terms "polymer" or "polymer resin" generallyinclude, but are not limited to, homopolymers, copolymers, such as, forexample, block, graft, random and alternating copolymers, terpolymersetc. and blends and modifications thereof. Furthermore, unless otherwisespecifically limited, the terms "polymer" or "polymer resin" shallinclude all possible symmetrical structure of the material. Thesestructures includes, but are not limited to, isotactic, syndiotactic andrandom symmetries.

The terms "melt flow" as used herein is the amount, in grams, of athermoplastic resin which can be forced through a given orifice under aspecified pressure and temperature within ten minutes, pursuant to ASTMD 1238-79. The term "melt flow index" as used herein is the amount, ingrams, of a thermoplastic resin which can be forced through a givenorifice under a specified pressure and temperature within ten minutes,pursuant to condition E of ASTM D 1238-79.

The terms "outer" or "outer layer" or "skin" or "skin layer" as usedherein means a layer of a multi-layer film which comprises surfacethereof.

The term "inner" or "inner layer" as used herein refers to a layer of amulti-layer film which is not a skin or outer layer of the film.

The term "core" or "core layer" as used herein refers to an inner layerof a multi-layer film having an odd number of layers wherein the samenumber of layers is present on either side of the core layer.

The term "intermediate" or "intermediate layer" as used herein refers toan inner layer of a multi-layer film which is positioned between a corelayer and an outer layer of said film.

The term "palindromic" film as used herein refers to a multi-layer film,the layer of which is substantially symmetrical. Examples of palindromicfilms would be film having the following layer configurations A/B/A, orA/B/B/A or A/B/C/B/A, etc. An example of a non-palindromic film is aA/B/C/A.

As used herein and unless otherwise specifically indicated, the term"cross-linking" refers to either irradiating the extruded film asdescribed in the detailed description of the invention or suitablyadditivating the polymers to be extruded so that the desired degree ofcross-linking is achieved in the extruded film.

As used herein the term "polyolefin" refers to thermoplastic polymersobtained by polymerization or copolymerization of relatively simple (C₂-C₁₂) olefins which may contain other comonomers wherein the olefinunits are however present in higher amounts with respect to the othercomonomers; including, but not limited to, homopolymers, copolymers,terpolymers blends and modifications of such relatively simple olefins.

Are specifically included therein homopolymers such as polyethylene andpolypropylene, copolymers such as propylene copolymers,ethylene-alpha-olefin copolymers, ethylene-vinyl-acetate copolymers, andethylene-acrylate or ethylene-metacrylate copolymers.

The term "polyethylene" as used herein refers to a family of resinsobtained by polymerizing the gas ethylene, C₂ H₄. By varying thecatalysts and methods of polymerization, properties such as density,melt index, crystallinity, degree of branching and molecular weightdistribution can be regulated over wide ranges.

Polyethylenes having densities below about 0.925 g/cm³ are called lowdensity polyethylenes (LDPE), those having densities ranging from about0.926 g/cm³ to about 0.940 g/cm3 are called medium density polyethylene(MDPE) and those having densities ranging from about 0.941 g/cm to about0.965 g/cm and over are called high density polyethylenes (HDPE).

The molecular structure of conventional LDPE is highly branched. Whileconventional MDPE possess a molecular structure which is branched, thedegree of branching is less than that of conventional LDPE. Themolecular structure of HDPE possesses little or no side branching.

The term "polypropylene" refers to a thermoplastic resin obtained byhomopolymerizing propylene units according to known processes. The term"propylene copolymers" refers to a propylene copolymer with ethyleneand/or butene-1 wherein the propylene units are present in a higheramount than the ethylene and/or butene-1 units. The term"ethylene-alpha-olefin copolymer" refers to a copolymer of ethylene withone or more (C₄ -C₁₂)alpha-olefin preferably selected from the groupcomprising the linear copolymers or terpolymers of ethylene with1-butene, 4-methyl-l-pentene, 1-hexene, and 1-octene. In particular, asused, herein linear low density polyethylene (LLDPE) has a densityusually in the range of from about 0.915 g/cm³ to about 0.925 g/cm³ ;linear medium density polyethylene (LMDPE), as defined herein, has adensity usually in the range of from about 0.926 g/cm³ to about 0.941g/cm³ ; while very low density polyethylene, (VLDPE), as used herein,has a density lower than 0.915. The melt flow index of linear low,medium and very low density polyethylenes generally ranges from betweenabout 0.1 to about 10 grams for ten minutes, preferably from about 0.5to about 3.0 grams for ten minutes. Linear low, medium and very lowdensity polyethylene resins of this type are commercially available orcan be manufactured by known methods.

Said terms also include-the so-called metallocene (or single-site orconstraint-geometry) linear polyethylenes having a density within theabove indicated ranges.

The term "ethylene vinyl acetate copolymer" (EVA) as used herein refersto a copolymer formed from ethylene and vinyl acetate monomers whereinthe ethylene derived units in the copolymer are present in major amountsand the vinyl acetate derived units in the copolymer are present inminor amounts.

As used herein, the term "ethylene-acrylate or ethylene-methacrylatecopolymer" refers to the product obtained by copolymerization ofethylene with acrylate monomers of formula ##STR1## wherein R ishydrogen or a methyl group and X is hydrogen, (C₁ -C₄)alkyl or a metalcation, preferably selected from Na⁺ and Zn⁺⁺, wherein the ethyleneunits are present in a higher amount than the acrylate units.

All compositional percentages used herein are calculated on a "byweight" basis.

Density should be measured at 23° C. and in accordance with ASTM D1505-68 (reapproved 1979).

Free shrink should be measured in accordance with ASTM D 2732.

Shrink tension and orientation release stress should be measured inaccordance with ASTM D 2838-81.

The tensile properties of the film should be measured in accordance withASTM D 882-81.

The elongation properties of the film should be measured in accordancewith ASTM D 638.

The haze and luminous transmittance of the film should be measured inaccordance with ASTM D 1003-61 (reapproved 1971).

The specular gloss of the film should be measured in accordance withASTM D 2457-70 (reapproved 1977).

The tear propagation of the film should be measured in accordance withASTM D 1938-67 (reapproved 1978).

The impact resistance of the film should be measured in accordance withASTM D 3420-80.

One method of determining whether a material is "cross-linked" is toreflux the material in boiling toluene or zylene, as appropriate, forforty (40) hours. If a weight percent residue of at least 5 percentremains, then the material is deemed to be cross-linked. A procedure fordetermining whether a material is cross-linked is to reflux 0.4 g of thematerial in boiling toluene or another appropriate solvent, for examplexylene, for twenty (20) hours. If no insoluble (gel) remains, thematerial may not be cross-linked. However, this should be confirmed bythe "melt-flow" procedure below. If, after twenty (20) hours ofrefluxing insoluble residue (gel) remains the material is refluxed underthe same conditions for another twenty (20) hours. If more than 5 weightpercent remains upon conclusion of the second refluxing the material isconsidered to be cross-linked. Preferably at least two replicates areutilized.

Another method whereby cross-linking and the degree of cross-linking canbe determined is by ASTM D 2765-68 (Reapproved 1978). Yet another methodfor determining whether a material is cross-linked is to determine themelt-flow of the material in accordance with ASTM D 1238-79 at 230° C.and while utilizing a 21,600 gram load. Materials having a melt flow ofgreater than 75 grams for ten minutes are deemed non-cross-linked. Thismethod should be utilized to confirm the "gel" method described abovewhenever the remaining insoluble residue (gel content) is less than 5%by weight, since some cross-linked materials will evidence a residualgel content of less than 5 weight percent. If the cross-linking isaccomplished by irradiation of the film the amount of ionizing radiationwhich has been absorbed by a known film material can be calculated bycomparing the weight percent of insoluble material (gel) remaining afterrefluxing the sample to the weight percent of gel remaining afterrefluxing standards of the same material which have been irradiated todifferent known degrees. The experts in the field also recognize that acorrelation exists between the amount of ionizing irradiation absorbedand the melt flow of material. Accordingly, the amount of ionizingirradiation which a material has absorbed may be determined by comparingthe melt flow of the material to the melt flow of the samples of thesame material which have been irradiated to different known degrees.

The term "gauge" is a unit of measure applied to the thickness of filmor the layers thereof. 100 gauge is equal to 1 ml, which is onethousandth of an inch (1 inch=2.54 cm).

A rad is the quantity of ionizing radiation that results in theabsorption of 100 ergs of energy per gram of a radiated material,regardless of the source of the radiation (1 rad=10⁻² Gy). A megarad is10⁶ rads (MRad is the abbreviation for megarad).

SUMMARY OF THE INVENTION

It has now been found a process for the manufacture of multi-layeredheat-shrinkable cross-linked polyolefin films containing recycle scrapsof the same film.

Particularly it has been found that, by recycling scraps of cross-linkedmultilayer heat-shrinkable polyolefin films in an inner layer of thesame film, a film is obtained which has physical properties andpackaging performances almost comparable to those of the virgin film.

In a general embodiment the process of the present invention comprisesthe steps of:

a) coextruding a multilayer polyolefin film in the form of a "tape";

b) cross-linking it; and

c) orienting said irradiated tape into a heat-shrinkable film,characterized in that scrap material produced in the manufacture or inthe further processing to finished articles of cross-linked films ofthis same structure is recycled into said step a).

OBJECTS OF THE PRESENT INVENTION

Accordingly, it is a general object of the present invention to providea process for the manufacture of cross-linked heat-shrinkable polyolefinfilms comprising the recycling of scraps of said cross-linked film.

Another object of the present invention is to provide a cross-linkedheat-shrinkable polyolefin film suitable for packaging food and non-foodgoods.

A further object of the present invention is to provide packagingmaterial, for example bags, pouches, comprising a film obtainedaccording to the process herein disclosed.

The process according to the present invention provides severaladvantages when compared to the processes of prior art. Firstly, thepresent invention allows to recycle scraps of cross-linked films, whichrecycling was taught to be impossible by prior art. Another advantage isin that the so obtained film has constant qualitative characteristics,comparable to the virgin film.

Both on-line and off-line recycling techniques may be used in theprocess according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a process of manufacturingheat-shrinkable multi-layer cross-linked polyolefin films characterizedin that one or more of the inner layers of said films contain recyclecross-linked polyolefin scraps.

The process of the present invention is a conventional process ofmanufacturing heat-shrinkable multi-layered polyolefin films, asdisclosed in the above cited prior art.

Every method of recycling scraps available in the art is suitable forthe process of the invention.

According to the invention, the multilayered film is composed of atleast three layers comprising one core layer sandwiched between twoouter layers. The film can be a palindromic film, with the two outerlayers one equal to the other, or can be asymmetric with the two outerlayers different one from the other.

When a number of layers of more than three layers is provided in thefilm, the core layer is herein intended as the central core of themulti-layered structure.

In a typical embodiment of the present invention the process begins byblending, if and as necessary, the raw materials (i.e. the polymericresins) in the proportions and ranges according to the desired film. Theresins are usually purchased from a supplier in pellet form and can beblended in anyone of a number of commercially available blenders as iswell known in the art. During the blending process any conventionaladditives and/or agents which are desired to be utilized are alsoincorporated. The additives may be incorporated by utilizing amasterbatch containing small percentages of the additives.

Additives which can conventionally be used include anti-fog,antioxidant, antistatic, slip and anti-block agents, thermalstabilizers, U.V. stabilizers, organic and inorganic pigments, and thelike agents. Preferred anti-block agents are diatomaceous silica (SiO₂,which is available for example from Mc Cullogh Benton, Inc.) andsynthetica silica such as those manufactured and marketed by W. R. GraceDavison Division under the trade name Syloid or Sylobloc. A preferredslip agent is erucamide (available from Humko Chemical). Other slipagents such as steraramide (available from Humko Chemical), behenamideN,N'-dioleylethylenediamine (available from Glyco Chemical) may beutilized. A preferred antioxidant and thermal stabilizing agent istetrakis methylene 3-(315'-di-t-butyl-4'-hydroxyphenyl)propionate!methane (available fromCiba-Geigy). Suitable antifog agents are polyoxyethylene sorbitanesters, glycerol fatty acid esters, and polyoxyethylene alkyl esterssuch as those commercially available under the trade names Atmer.Preferred antistatic agents are polyoxyethylene amines (such as Atmer163) or polyoxyethylene fatty alchols (e.g. Atmer 178).

The resins and applicable additives and/or agents are then fed to thehoppers of extruders which feed a coextrusion die. Depending on thestructural architecture of the multi-layer film, the number of extruderswill be determined by the expert in the field. When extruding through around die, the materials are coextruded as a relatively thick tube or"tape" which has an initial diameter and thickness dependent upon thediameter and die gap of the coextrusion die. If desired, a fine mist ofa silicone or anti-fog spray may be applicated to the interior of thefreshly extruded tubolar material to further improve processability ofthe tubular material, as disclosed, for example in EP-A-0071349. Thefinal diameter and thickness of the tubular film is dependent upon theracking ratio, i.e. the stretching ratio. As an alternative to tubularcoextrusion, slot dies, could be used to coextrude the material in sheet(or tape) form. Well-known single or multi-layer extrusion coatingprocesses could also be utilized, if desired. Exemplary of this methodis U.S. Pat. No. 3,741,253.

When cross-linking is achieved chemically a suitable amount ofcross-linking agents (e.g. peroxides) is added to the polymers to beextruded and no specific additional step is required.

When, according to a preferred embodiment of the invention,cross-linking is achieved by irradiation, said step is carried out afterextrusion by bombarding the film in its "tape" or unexpanded tubing orsheet form with high-energy electrons from an accelerator. Irradiationmay be accomplished by the use of high-energy radiation using electrons,which is the preferred radiation, but X-rays, -gama rays, beta rays,etc. can also be used. The electron irradiation: source can be a Van derGraaf electron accelerator, e.g. one operated, rated, for example atabout 2,000,000 volts, with a power output of about 500watts.-Alternatively, there can be employed other sources of high energyelectrons such as the General Electric 2,000,000 volt resonanttransformer or the corresponding 1,000,000 volt, 4 kilowatt, resonanttransformer. The voltage can be adjusted to appropriate levels which maybe, for example, 1,000,000 or 2,000,000 or 3,000,000 or 6,000,000 orhigher or lower. Other apparatus for irradiating films are known tothose expert in the field. The irradiation is usually carried out atbetween 1 megarad and 12 megarad. Preferably irradiation is carried outat between about 1 and about 6 MRad. Most preferably between about 1 andabout 4 MRad. Irradiation can conveniently be carried out at roomtemperature, although higher and lower temperatures, as for example,from 0° C. to 60° C. may be employed.

In the next step, the film is reheated to its orientation temperaturerange and oriented with a well-known orienting technique. For example,the heated film is inflated, by application of internal air pressure,into a bubble thereby transforming the narrow tape with thick walls intoa wide film with thin walls of the desired film thickness and width.This process is sometimes referred as "trapped bubble technique" or"racking". The degree of inflation and subsequent stretching is oftenreferred to as the "racking ratio" or "stretching ratio". Afterstretching, the tubular film is then collapse into a superimposedlay-flat configuration and wound into rolls often referred to as "millrolls".

Films scraps, which, as seen before, may be generated at differentstages of the-overall process, are gathered, suitably comminuted andrecycled. Film scrap can be recycled in any and in more than one of theinner layers of the original film structure or inner layer(s) of recyclefilm can be newly formed in the recycle containing film by dedicatingone or more extruders to melt process the recycle scrap and coextrudethe recycle layer(s) along with the coextrusion of the originalmultilayer structure.

The amount of film scrap in the recycle layer(s) may range from 5 to100% by weight of the layer(s) total weight.

The proportion of the scrap multilayer cross-linked film which mayglobally be incorporated into the inner layer(s) is however up to about50% by weight over the film total weight.

In case of a three layer original structure, in one preferredembodiment, scrap is recycled into the core layer, blended with virgincore polymer in amounts generally up to 75% of the core overall weight,preferably up to 50% and more preferably up to 35%.

In an alternative preferred embodiment two intermediate layers, betweenthe core and the outer layers are formed entirely of recycle scrap bydedicating one or two additional extruders to the melt processing ofsaid recycle scrap and giving rise to an increase in the overall numberof layers from 3 of the virgin structure to 5 in the recycle-containingone.

In this case the core layer may also contain part of cross-linked filmscrap blended with virgin polymer.

In still another alternative embodiment, in the recycle-containingstructure the core layer can be splitted into two layers and in betweena new layer entirely composed of recycle scrap can be coextruded.

Also in this case recycle scrap can also be added in the other innerlayers blended with virgin polymer.

Analogously, in the case of films containing more than three layers,film scrap may be recycled in one or more inner layers, in percent byweight of from 5 to 100% of the weight of the layer(s) and/or additionallayer(s) of film scrap can be formed up to a maximum total recycle ofabout 50% of the film weight.

Preferably, in the case of a five layer film structure, the film scrapwill be recycled in the core and/or in the two intermediate layers in abalanced amount. For recycling, scraps are either pre-blended with thevirgin material of the inner layer(s) or directly added into theselected extruders.

The scrap material which may be added up to a maximum amount of 50% w/vof the total structure, is preferably added up to 35% and morepreferably up to 25% of the total structure.

The process of the present invention is generally applicable tomulti-layers heat-shrinkable cross-linked polyolefin films.

Examples of said films may be found in EP-A-0 561 428, published22.09.93, U.S. Pat. No. 4,551,380, published Nov. 5, 1985, all in thename of the applicant; U.S. Pat. No. 4,865,902 assigned to E. I. Du Pontde Nemours and Company. In the above films the outer layers are mainlycomposed of low density polyethylene, medium density polyethylene, highdensity polyethylene, linear low density polyethylene, linear mediumdensity polyethylene, very low density polyethylene, ethylenevinylacetate copolymers or of blends thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the process of the present invention, a heat-shrinkablefilm was manufactured recycling scraps of the same film in the core ofthe manufactured film.

Particularly, the process of the present-invention is applied to anoriented, heat-sealable, cross-linked, multi-layer film comprising:

a core layer, consisting essentially of a LLDPE; and two outer layerseach comprising a three component blend of (1) a LLDPE, (2) a LMDPE, (3)an EVA copolymer.

This multi-layer film is disclosed in U.S. Pat. No. 4,551,380, issuedNov. 5, 1985 and assigned to the applicant.

A more preferred embodiment is represented by embodiments I, II and III,disclosed in the above U.S. Pat. No. 4,551,380; embodiment II being themost preferred herein.

A standard film (Film A) was prepared according to embodiment II of thedisclosure of U.S. Pat. No. 4,551,880. Said film was irradiated at anaverage MRad of about 2.0±0.5 MR.

Estrusions were carried out to incorporate recycled Film A scraps in thestandard structure. The scraps were pelletized and blended off-line withthe virgin core polymer.

Accordingly, four films containing scraps were prepared: the firstcontaining 10% of recycled scraps in the core (referred to as Film B);the second containing 5% of recycled scraps in the core (referred to asFilm C) the third containing 10% of recycled scraps in the skin(referred to as comparative Film D); the fourth containing 5% ofrecycled scraps in the skin (referred to as comparative Film E). Each ofthe four films was prepared with a thickness of 15 and 19 μm,respectively.

The four films were examined as to their optical properties incomparison with standard film A (hereinafter abbreviated as STD).

The results are shown in the following Table 1.

                  TABLE 1    ______________________________________              COMP.   COMP.    SAMPLE    FILM D  FILM E   FILM B                                     FILM C STD    ______________________________________    HAZE %    6.7     5.3      2.8   2.9    2.6    GLOSS (i = 60              103     111      133   130    135    degrees) gloss    units    ______________________________________

As shown in the above table, only Film B and Film C, namely the filmscontaining recycled scraps in their core layer, have good opticalproperties, suitable for use in packaging for display purposes.

An evaluation of the shrink quality of the films was performed. Theevaluation was carried out on packs made with a Gramegna semiautoL-sealer. The packs were shrunk in a Sitma tunnel at differenttemperatures. The samples were compared to STD which showed a goodshrink quality at 180° C.

The following tests were carried out only on Film B and Film C.

A physical characterization was carried out. Tables 2 and 3 report thequalitative results.

                  TABLE 2    ______________________________________    Physical evaluation    Film B/Film C (15 micron) vs STD    ______________________________________    Modulus:   Both are similar and higher than STD.    Tensile strength:               Similar to STD.    Elongation:               Higher than STD.    Tear properties:               Tear propagation and initiation resistance               are higher than STD    Kinetic coefficient               Lower for film to film conditions and    of friction:               equivalent for film to metal conditions.    (Dynamic)  STD stress conditions: similar to    Trim seal strength:               STD. High stress conditions:               higher than STD.    ______________________________________

                  TABLE 3    ______________________________________    FILM B/FILM C (19 micron) vs STD    ______________________________________    Modulus:        Similar to STD.    Tensile strength:                    Similar for L direction and                    slightly lower for T direction than                    STD.    Elongation:     Slightly lower than STD.    Tear properties:                    Tear propagation is quite similar                    to STD.                    Tear initiation is lower in both                    directions for Film B. Film C is                    equivalent in TD and slightly                    lower in LD.    Free shrink:    No significant difference.    Shrink tension: LD: higher than STD;                    TD: slight1y higher for Film C.    Optics:         Haze and gloss are similar to STD    Tack:           No tack was detected for all the                    structures.    Kinetic coefficient                    Both film to film and film to metal    of friction:    conditions are similar to STD    (Dynamic)    Trim seal strength:                    Considering STD and high stress                    conditions, the results are                    higher than STD.    ______________________________________

The above results show that the physical properties of the filmsobtained according to the present invention have physical propertiescomparable to STD.

The sealability was evaluated on a Pulsar hot bar sealer at thefollowing conditions:

    ______________________________________    sealing time         0.5 sec    sealing pressure     2.0 bar set                         1.5 bar actual    ______________________________________

Results are summarized in the following Table 4

                  TABLE 4    ______________________________________              SEAL BEHAVIOUR              (°C.)    FILM CODE   STICK       SEAL    MELT    ______________________________________    Film B 15/μm                115         120     150    Film B 19/μm                120         125     175    Film C 15/μm                115         120     150    Film C 19/μm                120         125     175    ______________________________________

The heat seal range for MR 15 and 19 micron is 125-165° C.

The shrink range was evaluated using cardboard boxes packed on aGramegna semiauto L-sealer.

The packs were then shrunk in a Sitma tunnel at different temperatures.

The samples were compared with STD.

    ______________________________________    Film Code        Shrink Range (°C.)                                  Burnt Through (°C.)    ______________________________________    Film B  15/μm 150-200      210    Film B  19/μm 150-210      220    Film C  15/μm 150-200      210    Film C  19/μm 150-210      220    STD     15/μm 140-200      210    STD     19/μm 150-210      220    ______________________________________

The results show no significant difference among the formulationsevaluated, the shrink range is wider for 19 micron films (60° C. vs 50°C.).

The packaging appearance was evaluated on the samples packed asdescribed above.

The samples were compared to STD which showed "good" shrink qualities.

At 180° C., no difference was noticed between the experimentalformulations and STD.

As to optical properties after shrink, STD performed slightly betterthan Film B and Film C, which appeared to be less glossy.

The samples tested performed similarly to STD, with respect to the trimsealing properties, heat seal range and shrink range.

From the above results, it can be seen that the process of the presentinvention allows to obtain heat shrinkable irradiated films containingrecycle scrap of the same film. The film obtainable from the processherein disclosed has physical and packaging characteristics which makeit comparable to standard films.

Therefore, packaging materials comprising a film obtainable by theprocess herein disclosed are within the frame of the present invention.

It should be understood that the detailed description and specificexamples which indicate the presently preferred embodiments of theinvention are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those of ordinary skill in the art upon review of theabove detailed description and examples.

What is claimed is:
 1. A multilayer, cross-linked, heat-shrinkable filmcomprising:a) at least one inner layer comprising thermoplastic polymer;and b) two outer layers comprising thermoplastic polymer different fromthe thermoplastic polymer of said at least one inner layer;characterizedin that cross-linked scrap material produced in the manufacture of theheat shrinkable film is incorporated into at least one of the inner orouter layers in an amount up to 50% by weight of the total film weight.